There are occasions when it is desirable to transmit and receive at a single location microwave signals having the same angle of arrival. This can be done by using a reflector antenna with a single feed and providing a circulator for transmit/receive capacity, or by providing the reflector antenna with two orthogonally-polarized side-by-side feeds. The former expedient increases the cost and intricacy of the installation, and the latter introduces an angle of "squint" between the directions of transmission and reception.
One of the known ways of constructing a radiation emitter or receiver at millimeter wave-lengths is known as the microstrip patch radiator, in which a transmitting or receiving patch is formed on the top of a microstrip circuit and connected by an impedance transformer to a conductor formed on the strip, the lower surface of the strip providing the necessary ground plan.